1. Field of the Invention
The present invention relates to an image information reading apparatus adapted to read information on an original placed on an original holding board by reciprocatably displacing an image reading unit which comprises a light source, an optical system, photoelectrical conveying means and other components, wherein improvement is achieved for the purpose of facilitating operations of assembling, maintaining and inspecting and moreover controlling is properly effected for a cooling fan which is accommodated in the frame of the apparatus.
2. Description of the Prior Art
In the recent years, a thermal transfer type color copying machine for carrying out color copying with the use of a strip of thermal transfer ink ribbon having a plurality of color inks coated thereon has been increasingly put in practical use. The conventional color copying machine is generally constituted by the combination of an image information reading apparatus (scanner section) adapted to read information on an original and an image building section (printer section) for building an image on a sheet of paper in response to image information which has been transmitted from the image information reading apparatus. Specifically, the image information reading apparatus is so constructed that image information on the original placed on the original holding board is read as color signal of light beam by optically scanning the original and thus read image informatin is transmitted to the image building section. On the other hand, the image building section is so constructed that on receipt of image information transmitted from the image information reading apparatus it is converted to color information corresponding to each of inks on the thermal transfer ink ribbon, a corresponding ink section on the thermal transfer ink ribbon is selected in dependence on thus converted color information and ink on the selected ink section is thermally transferred to a sheet of paper by means of a thermal head whereby color copying is achieved by successively transferring plural colors to the paper one by one.
Recently, a variety of development works have been conducted in order to design the whole image information reading apparatus to be used for a thermal transfer type color copying machine in smaller dimensions so as to allow it to be easily carried and place on a table or the like by an operator himself.
To facilitate understanding of the present invention description will be made below as to the conventional apparatus with reference to FIGS. 1 to 3. As shown in FIG. 1, a frame 1 for the apparatus is constructed by the combination of an opposing pair of side frames 2 made of U-shaped extruded sheet material, a front frame 3 and rear frame 4 which are separately fabricated and then assembled in the illustrated integral structure. When an original holding glass plate 5 serving as original holding board is placed on the upper surface of the frame 1, its both side edges are supported on both the side frames 2 while extending therebetween. At this moment the horizontal posture of the glass plate 5 has a significant effect on accuracy of assembling operation of the frame 1. For the reason there is a necessity for correctly locating components constituting the apparatus when assembling the latter or adjusting the focussed state of an optical system in the apparatus after completion of assembling operation. This leads to a problem that assembling operation of the apparatus is complicated, troublesome and time-consuming.
Usually, a tubular light source, for instance, fluorescent lamp is hitherto employed as light source which is accommodated in the image information reading apparatus. When the fluorescent lamp 6 is to be fitted into an image reading unit 7 in the casing of the apparatus, it is inserted into the interior of the casing through a circular hole 8 which is formed on the one side frame 2 of the frame 1, as shown in FIG. 2. Namely, when the fluorescent lamp 6 is fitted into the unit 7, the conventional steps of operations are such that the glass plate 5 is first removed from the side frames 2, the fluorescent lamp 6 is inserted through the hole 8 and it is firmly supported in position in the frame 1 with the aid of operator's hands which are inserted through the rectangular opening on the upper surface of the frame 1. As is well known, brightness of the fluorescent lamp 6 varies across the whole length thereof in such a manner that it generates a reduced intensity of light at both the end parts and it does a normal intensity of light in the central part. For the reason, when a fluorescent lamp is employed for a color copying machine, only the central part thereof where a substantially uniform intensity of light is generated is utilized as an effective part with the exclusion of both the end parts in view of the fact that intensity of light generated by it and color balance have a significant effect on image building. For instance, it is assumed that a fluorescent lamp of which total length l is 304 mm and of which distance l.sub.0 between both filaments is 288 mm is used for the apparatus, when an original having A4 size is scanned in the longitudinal direction. In this case the effective length l.sub.0 is shorter than the distance l.sub.1 between both the filaments.
For the reason the conventional apparatus is so designed that width L.sub.1 of the rectangular opening on the upper surface of the frame 1 is determined substantially same to the effective length l.sub.0 of the fluorescent lamp 6 and width L.sub.2 of the image reading unit 7 is determined substantially same to the total length l of the fluorescent lamp 6. Thus, it is impossible to mount and dismount the image reading unit 7 and fit and remove the fluorescent lamp 6 from the operative area located above the upper surface of the frame. Accordingly, mounting and dismounting operations as well as replacing operations are very troublesome and complicated to be performed.
Usually, the conventional image information reading apparatus is equipped with a cooling fan for the purpose of preventing excessive increase of temperature in the casing of the apparatus due to generation of heat from fluorescent lamp and other components. However, in the conventional apparatus the cooling fan is caused to rotate at a constant rotational speed during operation of the apparatus after electricity supply source is turned on. This leads to a problem that the cooling fan generates an increased magnitude of noisy sound during waiting state of the apparatus. To reduce generation of noisy sound during waiting state of the apparatus it is already proposed that the cooling fan has a reduced number of revolutions but this leads to another problem that the fluorescent lamp is excessively heated up to an elevated temperature during reading operation (during copying operation).